Along with development of wireless multimedia services, requirements of people on high data rate and user experiences increasingly grow, so that higher requirements on system capacity and coverage of a conventional cellular network are made. On the other hand, requirements of people on knowing about and communicating with interested persons or things nearby gradually increase along with prevailing of applications such as a social network, short-distance data sharing and local advertising; and here, the application service such as the social network, short-distance data sharing and local advertising is called proximity service. A conventional cell-based cellular network has obvious limitations in terms of support to high data rate and proximity service, and under such a requirement background, a D2D technology representative of a new direction of future development of communication technologies emerges. Application of a D2D technology may reduce a burden of a cellular network, reduce battery power consumption of User Equipment (UE), increase data rate, improve robustness of a network infrastructure and well meet requirements on a high-data rate service and proximity service.
A D2D technology may work in an authorized frequency band or an unauthorized frequency band, and allows direct discovery/direct communication of multiple pieces of D2D UE with a network infrastructure or without a network infrastructure. There are mainly three D2D application scenarios as follows:
1) UE1 and UE2 perform data interaction under coverage of a cellular network, the cellular network is a network covered by an Evolved Node B (eNB), and a user plane data interaction process is implemented without a network infrastructure, as shown in mode 1 in FIG. 1;
2) UE in a weakly-covered/uncovered area performs relay transmission, as shown in mode 2 in FIG. 1, and UE4 with poorer signal quality is allowed to communicate with the network through UE3 covered by the network nearby, which may help an operating company to extend coverage and improve capacity; and
3) direct communication among equipment is allowed under the condition that the cellular network may not work normally in case of an earthquake or emergency, as shown in mode 3 in FIG. 1, and a control plane and user plane among UE5, UE6 and UE7 may perform one-hop or multi-hop data communication without any network infrastructure.
A D2D technology usually includes a D2D discovery technology and a D2D communication technology:
1) the D2D discovery technology is configured to judge/determine proximity between two or more pieces of D2D UE, for example, judge/determine proximity between two or more pieces of D2D UE within a range where D2D direct communication is allowed, or is configured to judge/determine that first UE is proximal to second UE; and
2) the D2D communication technology refers to a technology for implementing direct communication of part or all of communication data between D2D UE without a network infrastructure.
In a cellular network coverage scenario, D2D communication resources are usually scheduled and allocated by an eNB, which may improve resource reusing efficiency and simultaneously ensure control of a network side over D2D communication and effects of interference coordination between D2D communication and cellular communication. Communication resources of D2D UE may be dynamically scheduled by an eNB, or the eNB may allocate and semi-persistently schedule resources to the D2D UE. In a public security scenario, D2D communication requires high robustness, and may maximally provide service under the current condition of communication resource shortage, congestion or network infrastructure paralysis. Therefore, public security requires D2D communication to work in a network coverage scenario and also work in partial coverage and out-of-coverage scenarios. In the out-of-coverage scenario, D2D UE may work in a self-organization manner, and shares the same resource pool with other D2D UE outside network coverage in a contention manner. The resource pool shared in the out-of-coverage scenario may be acquired from a prose function server or a network element of a core network when the UE is located within network coverage, and for example, is acquired from a proximity service application server.
UE within coverage of a cell is required to have a capability of performing cellular communication with a serving eNB and simultaneously performing D2D communication with D2D UE outside coverage of the serving eNB. For example, UE located on an edge of the cell may be required to transmit or receive D2D information of D2D UE outside the coverage of the serving eNB and simultaneously transmit or receive cellular data within the coverage of the serving eNB, or transmit D2D information by virtue of a resource scheduled by the serving eNB.
When a frequency point of a resource pool used outside coverage of a serving eNB is different from a frequency point used by cellular or D2D communication within the coverage of the serving eNB, UE without a Carrier Aggregation (CA) capability is required to work on the two different frequency points in a time division duplex manner. Moreover, when the UE works on the frequency point used by the resource pool outside the coverage of the serving eNB, the UE suspends reception or transmitting of cellular data of the serving eNB or scheduled D2D information, that is, it is impossible for the UE to perform cellular communication of the serving eNB and dynamically scheduled D2D communication, which makes quality of service of cellular communication and D2D communication and user experiences influenced.
When the frequency point of the resource pool used outside the coverage of the serving eNB is the same as the frequency point used by cellular or D2D communication within the coverage of the serving eNB, the UE may simultaneously monitor and receive D2D information within and outside the coverage of the serving eNB. However, since the UE may have only one radio frequency unit or there may exist a transmitting and reception self-interference phenomenon, D2D information of the same UE on the same frequency point is required to be received and transmitted in a time division manner, and the same UE on the same frequency point is also required to receive D2D information and transmit cellular data in the time division manner. Specifically, when UE receives information in the resource pool outside the coverage of the serving eNB, for example, the UE monitors and receives D2D information in the resource pool outside the coverage of the serving eNB, the serving eNB scheduling the UE to transmit cellular data or D2D information may bring interference to D2D information monitoring and reception of the UE in the resource pool outside the coverage of the serving eNB to reduce receiving performance of the UE and influence quality of service of D2D communication and user experiences.